This invention relates to polymer polyols, and particularly to polymer polyols containing high levels of dispersed polymer particles, and to a process for their production using a preformed dispersant.
Polymer polyols are dispersions of addition polymer particles in a continuous polyol phase. The presence of the addition polymer particles in the polyol imparts various desirable properties to polyurethanes, particularly flexible polyurethane foams, prepared from the polyol. In particular, the polymer particles act as a reinforcing filler and cell opener in the foam. The polymer particles also improve the ability of a reaction mixture containing the polymer polyol and a polyisocyanate to flow and fill a mold in the production of molded foams.
One problem with the polymer polyol is that the dispersed polymer particles tend to agglomerate and then settle out of the continuous polyol phase. It is therefore desirable to prepare the polymer polyol in such a way that the tendency of the particles to agglomerate is minimized. The most successful approach to date has been to employ a vinyl-unsaturated polyether which is copolymerized with the addition polymerizable monomers to form a dispersant or stabilizer.
For various reasons, it is desirable to prepare a polymer polyol having a high level of dispersed polymer particles. High levels of dispersed polymer particles provide enhanced reinforcement and cell opening. In addition, the production of high solids polymer polyols is economically advantageous, since a smaller amount is needed to obtain an equivalent amount of polymer particles. Thus, the user can purchase a smaller amount of a high solids polymer polyol and dilute it with an additional, less expensive polyol to obtain a lower overall solids level.
These high solids polymer polyols are especially prone to agglomeration and settling. The production of high solids polymer polyols has also been hampered by the high viscosity obtained when the solids level exceeds about 30% by weight. The practical upper limit on viscosity for these polymer polyols is about 12,000, preferably about 10,000 centipoises, since the pumping equipment used by foamers generally cannot handle higher viscosities at an acceptable rate or with acceptable accuracy. This limit, however, is often exceeded with conventional polymer polyols having high solids.
It would therefore be desirable to provide a process whereby a polymer polyol is formed which has a low tendency for its particles to agglomerate and settle out. It is further desirable to provide a polymer polyol which is prepared having, at a given solids level, a viscosity which is as low as possible. More particularly, it would be desirable to provide a process whereby a polymer polyol having 35% or more solids is prepared at a useable viscosity.